stacktrace: fix kernel-doc typo

Change @task to @tsk to prevent kernel-doc warnings:

kernel/stacktrace.c:138: warning: Excess function parameter 'task' description in 'stack_trace_save_tsk'
kernel/stacktrace.c:138: warning: Function parameter or member 'tsk' not described in 'stack_trace_save_tsk'

Link: https://lkml.kernel.org/r/20231220054945.17663-1-rdunlap@infradead.org


Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>